Process for oxidizing olefins to carbonyl compounds



3,459,644 PROCESS FOR OXIDIZING OLEFINS T CARBONYL COMPOUNDS Alexander F. MacLean and Adin L. Stautzenberger,

Corpus Christi, Tex., assignors to Celanese Corporation, a corporation of Delaware No Drawing. Filed Jan. 3, 1966, Ser. No. 517,959 Int. Cl. C071) 3/00; BOlk 1/00 11.5. Cl. 20480 7 Claims ABSTRACT OF THE DISCLGSURE Carbonyl compounds, including aldehydes, ketones, and carboxylic acids, are produced by the oxidative cleavage of an unsaturated olifinic hydrocarbon by a process which comprises contacting the hydrocarbon with a neutral to acidic aqueous solution of a catalyst comprising ruthenium together with a cerium salt having an oxidation potential greater than 1.5 volts. In a particular embodiment, the cerium salt oxidizing agent is regenerated electrochemically.

This invention relates to improvements in the process for the production of carbonyl compounds including carboxylic acids, aldehydes and ketones, by the oxidation of olefinic hydrocarbons. More particularly, this invention relates to a process for the oxidative cleavage of olefinic hydrocarbons to aldehydes in the presence of a ruthenium catalyst and an oxidizing agent, the oxidizing agent being regenerated by electrochemical oxidation.

There has been much work and activity recently on a new, continuous process for the catalytic oxidation of olefins to carbonyl compounds using a catalyst composed of a platinum group metal salt and a redox system. In US. Patent No. 3,080,425 there is disclosed a process for the production of aldehydes and ketones by contacting an olefin such as ethylene with an aqueous solution of a platinum metal catalyst in the presence of a multivalent metal salt redox agent having an oxidation potential higher than that of the platinum catalyst. The oxidation occurs without altering the number of carbon atoms present in the molecule, i.e. without oxidative cleavage of the olefin bond. In U.S. Patent No. 3,147,203 there is described a process for the production of aldehydes and ketones by oxidation of olefinic hydrocarbon in the presence of a platinum group metal followed by regeneration of the catalyst by electrochemical oxidation. Although ruthenium is disclosed as a catalyst in the processes of the two foregoing patents, the oxidation of the olefinic hydrocarbon takes place without altering the number of carbon atoms present in the molecule as ruthenium is employed in its lower oxidation state as Ru(III). In British Patent 900,107 there is described a process for the oxidation of organic compounds by ruthenium tetroxide, e.g. [Ru(VIII)]. The reaction of ruthenium tetroxide with olefins to give aldehydes with simultaneous carbon-carbon bond cleavage is discussed. The process is not a continuous process in that there is no provision for the regeneration of the ruthenium catalyst, and the efficiencies described are quite low.

We have found by the present process that carbonyl compounds, such as carboxylic acids, ketones and aldehydes can be obtained in good yield in a continuous manner, if desired, by contacting olefinic hydrocarbons with a catalytic amount of ruthenium in the presence of at least one oxidizing agent having a formal oxidation potential greater than 1.5 volts.

The oxidizing agents useful in the process of this invention include compounds of metals which appear in various oxidation states and which have formal oxidation potentials greater than 1.5 volts with reference to the standard hydrogen electrode. Compounds with potentials above about 1.5 volts are capable of oxidizing the lower states of ruthenium to ruthenium tetroxide [Ru(VIII)]. Some of the oxidizing agents which have been found applicable in this invention include compounds such as cerium perchlorate, cerium nitrate, cerium methanesulfonate, nitric acid and hypochlorous acid.

The ruthenium catalyst forms an addition compound or complex with the olefinic hydrocarbon, although the exact mechanism which cleaves olefins to aldehyde is speculative. The stoichiometric reaction requires a four electron change.

Substantially any olefinically unsaturated hydrocarbon which is free from steric hinderance may be used in the process according to this invention. Compounds which are most useful in the process according to this invention are olefins such as butene, propene, hexene, heptene, octene cyclohexene, styrene and their substituted homologs such as Z-methyl propene.

For a continuous process it is necessary to regenerate the oxidizing agent, which in turn facilitates the reformation of the higher oxidation state of the active ruthenium catalyst component necessary to carrying out the reaction. Certain of the oxidizing agents applicable to the process of this invention can be regenerated by electrochemical oxidation. For example, solutions of cerium (IV) are conveniently made by electrolytic oxidation of cerium (III). In this process a diaphragm electrolytic cell need not be used. In an undivided electrolytic cell preferably used in the process of this invention, acid is used and must be replaced, however, the cell voltage required is usually lower than that required for a corresponding divided electrolytic cell; thus the use of an undivided or non-diaphragm cell usually results in cheap er operation. Electrodes which may be used for the electrochemical process include inert materials such as platinum, graphite, lead, tantalum and others. Cerium (III) is oxidized at the anode to cerium (IV) in either a divided or undivided cell while hydrogen gas is produce in an undivided cell and caustic in a divided cell at the cathode. The electrochemical oxidation of Ce(III) to Ce(IV) may be carried out at temperatures ranging from about 10 to C. and preferably from about 25 to 50 C. Anode current densities of 1040 milliamps per sq. cm. with cell terminal voltages of 3.2 to 3.5 volts are sufficient for high conversion rates.

The process according to this invention is preferably carried out in an aqueous system, however, the reaction media may be diluted with substances which act as coupling agents such as t-butyl alcohol or acetic acid which are inert under the reaction conditions. It is necessary that the reaction be carried out in a neutral to acidic medium. The reaction is substantially pH independent from a pH of 1 to 5. When an undivided electrolytic cell is used, acid is consumed during the reaction. This necessitates the addition of acid during the course of the reac tion to assure adequate pH control.

The process of this invention can be carried out at temperatures ranging from about 0 to 200 C. and preferably from 25 to 50 C. An increase in temperature results in a corresponding increase in reaction rate. At higher temperatures side reactions occur which lower the yields of desired products.

The process of this invention can be carried out at atmospheric pressure, at subatmospheric pressure or at superatmospheric pressure, e.g. pressures ranging from 0 to 1500 p.s.i. When a gaseous olefin is employed, pressures greater than atmospheric may be used to promote the solubility of the olefin in the aqueous reaction medium.

The molar ratio of ruthenium to the oxidizing agent employed is not particularly critical to this process. The amount of ruthenium necessary to catalyze the reaction is very small, ranging from about 1 1O Molar to 1 1O- Molar. The oxidizing agent need only be present in amounts sufficient to oxidize ruthenium to its active catalytic state, e.g. a ruthenium/oxidizing agent molar ratio of at least 1:1. An excess of olefin is normally used in the process of this invention to minimize secondary oxidation. The secondary oxidation which occurs in this instance is the oxidation of the aldehyde, formed as a result of the oxidation of the olefin, to the corresponding acid. To minimize this secondary oxidation a stirred two phase system may be used. In the case of a liquid olefin such as octene-l, which is oxidized to heptaldehyde in the presence of ruthenium [Ru(VII-I)], the heptaldehyde preferably concentrates in the olefin phase rather than the aqueous phase, thus minimizing secondary oxidation. In general, as long as the aldehyde concentration is minimized in the aqueous phase, it will be relatively free from further oxidation.

The process may be carried out by a batchwise or continuous process, although a continuous process is preferred. As an example of a continuous process, the following description is given. An oxidizing agent is fed to a reaction zone containing the desired olefinic hydrocarbon and an aqueous solution of ruthenium catalyst. As the reaction takes place the organic phase is removed from the reaction zone and continuously fed to a distillation column where the olefinic hydrocarbon is separated from the desired aldehyde product and recycled to the reaction zone. At the same time the aqueous spent oxidizing agent is recycled to the electrolytic cell for regeneration. Regeneration of the oxidizing agent may also be carried out in the reaction zone by electrochemical oxidation.

Many useful products can be obtained by the process of this invention. For example octene-l may be oxidized to give heptaldehyde and formaldehyde, heptaldehyde being a useful intermediate in the production of adipaldehyde and adipic acid, a useful nylon raw material intermediate.

Very favorable yields and efliciencies are obtained by this process. For example, current efiiciencies of about 50% were obtained for continuous operations in which heptaldehyde was continuously extracted from octene-l by distillation.

The following examples serve only to illustrate a number of the features of this invention and are not intended to limit the scope of this invention in any way.

EXAMPLE I A stirred electrolytic cell having an anode made of platinum gauze and a cathode of platinum wire was used as the reactor. A solution of 0.2 F cerium (III) in 1 N perchloric acid was added to the reactor-electrolytic cell. Three millifaradays of electricity were passed through the electrolyte. The current was 100 milliamperes and the cell voltage was about 2 volts. The current efficiency to ceric ion was about 90%. Twenty milliliters of octene-l and sufiicient ruthenium as ruthenium chloride were added to the reactor electrolytic cell. The concentration of ruthenium was 1 l0 F. The total aqueous phase was 80 milliliters. The reaction was allowed to proceed until the solution was colorless indicating the absence of cerium (IV), which has a yellow color. The temperature was about 25 C. The products obtained were analyzed and the following results obtained: 3.6 oxidation equivalents heptaldehyde, 6.27 oxidation equivalents formic acid, 0.48 equivalents formaldehyde. The efiiciency to heptaldehyde based on Ce(IV) was 36% The efiiciency to heptaldehyde based on octene-l was approximately 95%.

EXAMPLE II was carried out in nitric acid. In Run No. 2, methanesulfonic acid was used. In Run No. 3 acetic acid was added to the reaction media as a coupling agent or solubilizer. The higher proportion of heptanoic acid and formic acid indicates that secondary oxidation of the aldehyde to the corresponding acid occurred as the result of the, influence of the acetic acid coupling agent. In Run No. 4 a higher concentration of ruthenium was used. The efficiencies of the above indicated runs were calculated using 3.33 oxidizing milliequivalents as theoretical according to theequation TABLE I.CERIC OXIDATIONS OF OC'IENE-l IN A2- PHASE STIRRED SYSTEM ml. aqueous plus 20 ml. octane-1. Ceric pregenerated by electrolysis of 0.2 F Ge(III) in 1 N acid (pH=O)] Run 1 2 3 4 1 Nitric acid.

2 Methanesullonic acid.

3 Perchloric acid, 80% acetic acid. 4 Perchloric acid.

EXAMPLE III Employing the reactor-cell as described in Example 1 runs were made in which ceric was continuously reacted and regenerated electrolytically as shown by Table II. The runs were made by passing current through the well mixed octene-aqueous two phase mixture. The current density was adjusted to generate ceric (yellow color) at a rate approximating the organic oxidation rate. An attempt was made to keep the solution light yellow. After passing the desired quantity of electricity, the excess ceric was allowed to react to completion as indicated by decolorization. The products were removed and analyzed.

Run 1 was made with unpurified octene. Runs 2 and 3 gave very high current efiiciencies. In Run 4 the ruthenium concentration was reduced to 5 10 F and the temperature increased to 50 C. The conversion was relatively high and the current eificiency was 57%. TABLE II.GERIC OXIDATION OF OCTENE-l IN A TWO- PHASE SYSTEM CONCURRENT ELECTROLYTIC GEN- ERATION OF CERIO [Pt screen anode:100 sq. cm.; Pt wire cathode:1 sq. cm.; stgrretl diaphragmless cell; 80 ml. ag. phase; 20 ml. octeue p ase Run No 1 2 3 4 Ca charged, F 0.2 O. 2 0.2 0. 2 Bu charged F 100 100" 100 5X10c Current, milliamp 100-150 100 100 300-500 Cell potential, volt 2-2. 5 2. 0 1 9-2. 3 2-2. 5 Electricity, nullifaraday 3. 0 3. 0 3. 0 21. 0 H0104 electrolyte cone, molar 1. 0 1. 0 1. 0 1. 0 Temperature, C 25 25 25 50 Time of run, min 6O 60 60 70 Oil phase analysis, oxid. milliequivalent:

Heptaldchyde 0. 44 0. 0. 84 4. 0 Heptanoic acid 0 0. 9 Formic acid, calculated 0.88 1. 9 1. 68 8. 9 Current efficiency to heptaldehyde 2 44 95 84 57 Current accountability to above products, percent 44 95 84 66 1 CH2OVHCOOH assumed 2 Based on octane-Ha[0] heptaldehyde+ionnic acid. Ge generation current efficiency assumed to be 3 Ce generation current efficiency assumed to be 100%.

EXAMPLE IV Other olefins having low water solubility were reacted under conditions similar to those of Run 1 of Example III with concurrent ceric generation.

Heptene-3 was found to yield propionic acid and butyric acid instead of propionaldehyde and butyraldehyde because of the preference of the aldehydes for the aqueous phase in which secondary oxidation occurred.

Cyclohexene was oxidized to a mixture of adipaldehyde and adipic acid.

Methyl oleate was oxidized to give the following products according to the equation:

Nonanol was obtained along with some nonanoic acid. Alpha-pinene was oxidized to a mixture of products including pinonic aldehyde.

EXAMPLE V A reactor-column arrangement for the continuous production of heptaldehyde from octene-l was set up using the electrolytic cell-reactor arrangement as described in Example I. The conditions under which the reaction took place are shown by Table III. Heptaldehyde boils at 155 C. while octene-l boils at 121.3 C. Heptaldehyde produced from the reaction with octene-l was introduced at an intermediate point on a distillation column. The reboiler of the distillation column was kept at a tem perature sufiicient to remove unreacted octene-l overhead for recycle back to the reactor zone while the heptaldehyde was taken off at the bottom of the column.

TABLE III.OONTINUOUS PRODUCTION on HEPTALDE- HYDE FROM OCTENE-l [Pt screen anode=100 sq. cm.; Pt wire cnthode=1 sq. em.; aqueous solution, 80 ml.; octene in system, 80 ml.]

Run No 1 2 3 0.2 0.2 0. 2 3X10- 2X10- 300 300 1 100-500 Cell potential, volt. 2. 1 2-2 Electricity, millifaraday 7. 5 31 18 H0104 electrolyte, M 1.0 1.0 1.0 Temperature, C 42-49 45-47 49-52 Run time, m.in 90 290 140 Reboiler analysis,

Heptaldehyde 1. 44 4. 72 3.0 Heptanoic acid 0 0 Current efiiciency to heptaldehyde,

percent 57 46 50 1 300 average.

EXAMPLE VI Using the diaphragmless electrolytic cell and reaction conditions as described in Example I, octene-l was oxidized to heptaldehyde using manganese as the oxidizing agent for ruthenium instead of cerium. The manganese Was electrolytically regenerated.

EXAMPLE VII Twenty ml. of 0.096 M Ce(ClO in 1 N HClO containing 0.02 mg. of Ru C1 was agitated under an atmosphere of butene-2 gas. The Ce(IV) was reduced in a few minutes. Analysis of the mixture showed 0.58 millimole acetaldehyde which corresponds to 60% efiiciency based on Ce(IV).

EXAMPLE VIII A continuous run was made as described in Example V using n-hexane saturated with butene-Z as the liquid oil phase instead of heptaldehyde. From the reactor the liquid oil phase was passed to the middle of the distillation column and butene, acetaldehyde and some hexane removed overhead. Stripped hexane, from the base of the column, Was recycled to the reaction zone by way of a bubbler which saturated the hexane with butene-Z. The conditions and efiiciencies are given below.

Total aqueous inventory, ml. 280 Total hexane inventory, ml. 150 Approx. cone. of butene-2 in saturated hexane,

percent 25 Ce+ F. 0.5 Ru+ F. 6X10" Current, ma. 300 Cell potential, volts 2.3 Electricity, millifaradays 52 HClO electrolyte, N 2.0 Temperature, electrolytic cell, C. 25 Temperature, stirred reactor, C. 25 Product oxidation, meg acetaldehyde 16.6 Current efliciency to acetaldehyde, percent 32 The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for production of a carbonyl compound selected from the group consisting of aldehydes, carboxylic acids and ketones by the oxidative cleavage of an unsaturated olefinic hydrocarbon by contacting the olefinic hydrocarbon in a neutral to acidic media with a catalytic amount of a ruthenium (VIII) salt, the improvement which comprises performing the oxidation in the presence of an oxidizing agent having an oxidation potential greater than about 1.5 volts, the oxidizing agent being present in an amount suflicient to keep at least a portion of the ruthenium catalyst present as Ru(VIII).

2. Process according to claim 1 wherein the oxidizing agent is a metal salt.

3. Process according to claim 2 wherein the oxidizing agent i regenerated by electrochemical oxidation.

4. Process according to claim 3 wherein the electrochemical oxidation is carried out in an undivided cell at a temperature ranging from 10 to 85 C. and an anode current density of from 10 to 40 amps/sq. cm.

5. Process according to claim 4 wherein the contacting takes place at a temperature ranging from about 0 to 200 C.

6. Process according to claim 5 wherein the molar radio of ruthenium catalyst to oxidizing agent is at least 1: 1.

7. A continuous process for the production of a carbonyl compound selected from the group consisting of aldehydes, carboxylic acids, and ketones by oxidative cleavage of an unsaturated olefinic hydrocarbon which comprises contacting said olefinic hydrocarbon in the presence of a neutral to acidic aqueous catalyst solution comprising a ruthenium catalyst and a cerium salt whose oxidation potential is greater than 1.5 volts at a temperature of 0 to 200 C., removing the reaction products from the reaction zone as they are formed, and regenerating the cerium salt by electrochemical oxidation.

References Cited UNITED STATES PATENTS 3,048,636 8/1962 Grinstead 260-586 3,080,425 3/1963 Smidt et al. 260-586 3,087,968 4/1963 Htirnig et al 260-604 3,106,579 10/1963 Hornig et al. 260-58'6 3,122,586 2/1964 Berndt et al. 260-586 3,147,203 9/ 1964 Klass 204-80 3,152,586 10/1964 B'zinder et al 260-597 3,303,020 2/ 1967 Clement et a1 -83 JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner US. Cl. X.R. 260-597 

